An integrated three-phase ac charger for vehicle applications with dual-inverter drive

ABSTRACT

A powertrain for electric and plug-in hybrid vehicle applications with integrated three-phase AC charging featuring buck-boost operation and optional vehicle-to-grid (V2G) capability, along with corresponding methods and machine instruction sets for switch control. The powertrain can include of a three-phase current source converter (CSC) front-end with an associated input filter, a polarity inversion module, and in an embodiment, a dual-inverter motor drive. The dual-inverter drive is the source of both the back emf and requisite DC inductance for the CSC. A compact design is thus provided as no additional magnetics are required and the on-board cooling system required for traction mode can be re-deployed for charging and V2G mode. The powertrain is mode shifted between charging and V2G mode through an optional polarity inversion module.

CROSS REFERENCE

This application is a non-provisional of, and claims all benefit,including priority to, U.S. Application No. 62/725,711, filed on 2018Aug. 30, entitled “INTEGRATED BIDIRECTIONAL THREE-PHASE AC CHARGER FORVEHICLE APPLICATIONS”. This application is incorporated by reference inits entirety.

FIELD

Embodiments disclosed herein generally relate to power electronics forelectric and plug-in hybrid electric vehicle applications. Morespecifically, the embodiments relate to electric powertrains withintegrated charging capability.

BACKGROUND

One of the bottlenecks to widespread adoption of electric vehicles isthe time required to charge the on-board batteries. Generally, the powerto charge the vehicle batteries is supplied from either a low-voltagesingle-phase alternating current (AC) grid, three-phase AC grid ordirect current (DC) grid connection.

Unlike three-phase AC grids, low-voltage DC grids are not currentlywidely available; and compared to single-phase AC grids, three-phase ACgrids generally have higher availability of power. Three-phase gridconnections can be found where higher availability of power is requiredsuch as commercial buildings, office buildings and industrialfacilities, for instance. Additionally, new three-phase ac gridconnections can be made from existing three-phase distribution lines,for instance. Chargers for enabling three-phase AC charging can beeither off-board or on-board the vehicle.

On-board integrated charger solutions are advantageous in that they havethe potential to significantly reduce external infrastructure costs byintegrating all power electronics onto the vehicles and leveringexisting on-board cooling systems.

The main disadvantages of integrated on-board chargers are theadditional weight, volume, and cost to the vehicle, which are addressedby the presented solution.

SUMMARY

Electrical grid charging from DC sources is a simpler approach relativeto charging by AC grid infrastructure, but not always available.

AC grid infrastructure is more readily available but conversionapproaches have typically required expensive or cumbersomeinfrastructure elements for AC/DC conversion prior to use with anelectric vehicle or a hybrid-electric vehicle. For example, a AC/DCconversion stage can be conducted by an additional rectifier circuit,which, in certain situations, utilize magnetic components to improveefficiency of power flow/energy transfer.

This type of AC/DC conversion stage adds infrastructure complexity(e.g., if required at every AC grid interface at electric car chargingstations), and the magnetic components (e.g., inductors, capacitors) areboth cumbersome (e.g., these components take up limited space atcharging stations and are heavy) and expensive (e.g., additionalinductors can be especially expensive).

Electric or hybrid-electric vehicles are desirable relative toconventional combustion engine vehicles due to reductions in harmfulemissions. Combustion engines that utilize petrol or diesel can emittons of carbon dioxide among other harmful emissions, such as methane,nitrous oxide that potentially contribute to climate change. Electrichybrid engines can be adapted to use potentially both gasoline/dieseland electric power stored therein.

Presently, electric vehicle adoption is limited by sparse availabilityof electric vehicle charging stations, as the cost and spacerequirements (e.g., limiting the number of stalls) for current electriccar charging stations are high. Large distances between electric carcharging stations or queuing due to less stalls than a number ofvehicles to be charged can severely impact the viability of electriccars as electric vehicles only have limited range.

Accordingly, an improved approach for charging from an AC grid (e.g., amulti-phase AC grid) is desirable. The proposed approach is an improvedcircuit topology (and corresponding circuits, methods, and machineinstruction sets stored on non-transitory machine readable media) thatis directed to an environmental (green) technology that could help toresolve or mitigate environmental impacts by improving the viability ofelectric or hybrid vehicles. As the viability of electric or hybridvehicles is improved, reliance on combustion engines can be reduced tohelp conserve natural environment and oil/gas resources.

The magnetic components of the electric motor, when not in use, can beleveraged for AC/DC conversion. A proposed approach described herein isdirected to a electric powertrain circuit topology that includes acurrent source converter circuit that operates as an AC/DC conversionstage and couples to a dual inverter drive system that has two chargingstages (e.g., an upper charging stage and a lower charging stage, whichalso can be referred to as a first charging stage and a second chargingstage) that is connected across the motor (e.g., across motor windings).Because the dual inverter drive system connects through the motoritself, the magnetic components of the motor are used for the AC/DCconversion, providing a potentially less cumbersome and less expensiveapproach to AC/DC conversion. A stage is a circuit portion and includesphysical electrical circuit components.

The electric powertrain circuit, in some embodiments, is provided as acomponent of the electric or hybrid vehicle and can, for example, resideon or within the electric or hybrid vehicle (e.g., as a circuit that isdirectly coupled to the motor and energy storage devices) such that theelectric or hybrid vehicle can connect directly to three phase AC gridinterfaces, even if the AC grid interface does not have an availableAC/DC conversion stage, for example, when the electric or hybridvehicle's motor is not being used for locomotion. An additionalcontroller circuit can be provided that is configured to toggleoperation of the open wound motor between a locomotion state and aenergy flow state.

Further embodiments are described herein for polarity inversion suchthat the electric or hybrid vehicle is also able provide vehicle to grid(V2G) charging capabilities in different variant embodiments. Not allembodiments include vehicle to grid (V2G) chargingcapabilities—uni-directional charging from the AC grid to the electricor hybrid vehicle is contemplated in some embodiments. Alternatively,uni-directional charging to the AC grid from the electric or hybridvehicle is also contemplated in other embodiments. V2G charging isuseful, for example, in emergency situations, or situations where thegrid is isolated and remote (e.g., a rural grid). Depending on gridelectricity prices, it may also be economically advantageous to provideenergy to the grid.

The dual inverter drive system includes a upper charging stage and alower charging stage. Each of these stages has an energy storage andvoltage source converter. For example, the upper charging stage has afirst energy storage and a first voltage source converter (VSC1). Thelower charging stage has a second energy storage and a second voltagesource converter (VSC2). The dual inverter drive can be configured toprovide voltage boosting capability, enabling power to be exchangedbetween the AC grid and the first or second energy storages when a sumof the energy storage voltages is greater than the maximum averagerectified voltage across the CSC DC terminals.

An open wound motor (e.g., the motor that can be used for locomotion) iscoupled between the first voltage source converter and the secondvoltage source converter, and the open wound motor has three or moremotor windings. Each of these windings are coupled to a corresponding ACterminal of each of the first voltage source converter and the secondvoltage source converter.

The current source converter (CSC) includes three CSC AC phase terminalsfor coupling with the AC grid, a positive CSC DC terminal coupled to theupper charging stage at a positive VSC1 DC terminal, and a negative CSCterminal coupled to the lower charging stage at a negative VSC2 DCterminal.

The CSC includes a first circuit leg, a second circuit leg, and a thirdcircuit leg. Each circuit leg corresponds to a corresponding CSC ACphase terminal of the three CSC AC phase terminals, and has at least oneupper switch and one lower switch. The upper switches are each coupledto a corresponding CSC AC phase terminal and the positive CSC DCterminal. The lower switches are each coupled to a corresponding CSC ACphase terminal and the negative CSC DC terminal.

Each of the upper and lower switches are controlled by gate controlsignals, which when only one upper switch is in an on-state, that switchwill conduct a current equal to the sum of the three winding currents,and when only one lower switch is operated, that switch will conduct acurrent equal to the sum of the three winding currents. These gatecontrol signals control the energy flow between the AC grid and theelectric vehicle/hybrid electric vehicle, exploiting the inductance ofthe motor to enable operation.

The CSC is a three-phase current source converter (CSC) front-end thatcan operate optionally, in another embodiment, together with an inputfilter which exploits the inductance of the motor to enable operation.The powertrain components provide a variable back emf and a seriesinductance to the CSC. The upper and the lower switches of the CSC canbe configured in some embodiments such that both the real power andreactive power exchanged with the AC grid are separately controlled. TheCSC can provide voltage bucking capability, enabling power to beexchanged between the AC grid and the first or second energy storageswhen a sum of the energy storages is less than the maximum averagerectified voltage across the CSC DC terminals.

This re-use of the powertrain magnetics for the implementation of theintegrated charger has three benefits: 1) no additional magneticcomponents are required which would otherwise add significant weight andvolume to the charger; 2) motor cooling system is leveraged for coolingof the magnetics; and 3) the motor cooling system can be shared with theCSC front-end for cooling of the power electronic devices.

The energy storage elements are not restricted to being of a certaintype nor are the energy storage elements required to be of identicaltype. Some examples of energy storage elements, include: batteries, fuelcells and super-capacitors. In an embodiment, one energy storage elementcan be of battery type and the other of super-capacitor type. Due to theparticular arrangement of elements in an embodiment, the converteroperates as a three-port converter during both charging and V2G modes.The emfs for each of the three ports are: 1) energy storage element 1;2) energy storage element 2; and 3) the rectified AC grid voltage.

In an embodiment, the two independent energy storage elements connectedon either side of the motor via inverters are electrically in series forcharging and vehicle-to-grid mode. The ability to series connect theemfs is highly advantageous as the powertrain can realize higher dc-linkvoltages resulting in improved overall efficiency and increased chargingpower capability.

Another advantage to the use of a CSC for the front-end is that due tothe inherent bi-directional blocking capability of the switches of theCSC, the charging currents for the energy storage elements arecontrollable irrespective of state of charge and nominal energy storageelement voltages. The CSC can also feature fault-blocking capability,which ensures the energy storage elements are protected in the event ofan AC grid fault (e.g., AC short circuit). The AC grid can be optionallycoupled to the CSC through an input filter, the input filter configuredto filter out harmonic currents generated by the electric powertrainfrom entering into the AC grid.

The structure of a CSC front-end together with a variable back emfprovided by the differentially connected dual-inverter drive allows forbuck-boost operation for charging which is also highly advantageous. Inbuck-mode, the CSC front-end steps down the grid voltage; and inboost-mode, the dual-inverter drive steps-up the grid voltage.

The charger is switched between charging and vehicle-to-grid modethrough use of a polarity inversion circuit between the CSC and thedual-inverter drive. The role of the polarity inversion circuit is toinvert the polarity of the DC-side back emf generated by thedual-inverter drive. Note, the polarity inversion circuit is optional,and included only in some embodiments. For example, the polarityinversion circuit is not needed if V2G operation is not required. Thepolarity inversion circuit can be coupled between the CSC and the uppercharging stage and the lower charging stage such that the the polarityinversion circuit is coupled to the CSC at the positive CSC DC terminaland the negative CSC DC terminal, and the polarity inversion circuit iscoupled to the upper charging stage at the positive VSC1 DC terminal,and coupled to the lower charging stage at a negative VSC2 DC terminal.The polarity inversion circuit inverts a polarity of a back emf providedby the dual inverter drive such that the electric vehicle or thehybrid-electric vehicle is able to provide power to the AC grid.

In a first variant, the polarity inversion circuit is coupled to theupper charging stage at the negative VSC1 DC terminal and to the lowercharging stage at a positive VSC2 DC terminal, and includes at least oneswitch and that interfaces the CSC with the dual inverter drive, withthe polarity inversion circuit having a first state and a second state;the first state coupling the positive CSC DC terminal and the positiveVSC1 DC terminal, and coupling the negative CSC DC terminal and thenegative VSC2 DC terminal; and a second state coupling the positive CSCDC terminal and the negative VSC1 DC terminal, and coupling the negativeCSC DC terminal and the positive VSC2 DC terminal; wherein the in thefirst state, power is directed to the electrical vehicle or the hybridelectric vehicle and the in the second state, power is directed to theAC grid.

In a second variant, the polarity inversion circuit includes at leastone switch and interfaces the CSC with the dual inverter drive, with thepolarity inversion circuit having a first state and a second state; thefirst state coupling the positive CSC DC terminal and the positive VSC1DC terminal, and coupling the negative CSC DC terminal and the negativeVSC2 DC terminal; and a second state coupling the positive CSC DCterminal and the negative VSC2 DC terminal, and coupling the negativeCSC DC terminal and the positive VSC1 DC terminal; wherein the in thefirst state, power is directed to the vehicle and the in the secondstate, power is directed to the grid.

In either the first variant or the second variant, the polarityinversion circuit can include a mechanical switch of double pole singlethrow type or a switch of double pole double throw type. In either thefirst variant or the second variant, the polarity inversion circuitcould alternatively consist of at least four semiconductor switches witheach switch of the at least four semiconductor switches coupling one CSCDC terminal to one VSC DC terminal.

In a third variant, each phase of the CSC is associated with twoswitches, an upper switch corresponding to the phase and a lower switchcorresponding to the phase, each of the upper switch and the lowerswitch corresponding to the phase comprising a first and a second seriesconnected sub-switches with an accessible mid-point, the firstsub-switch providing positive voltage blocking capability and the secondsub-switch providing negative voltage blocking capability; and thepolarity inversion circuit includes a first three phase switch networkand a second three phase switch network, with each three phase switchnetwork including at least four switches, three switches for each phaseand one master switch that is to controllable; the positive CSC DCterminal and the positive VSC1 DC terminal are electrically bonded, andthe negative CSC DC terminal and the negative VSC2 DC terminal areelectrically bonded; and wherein the first three phase switch networkcouples the mid-point of the three upper sub-switches to the dualinverter drive; wherein the second three phase switch network couplesthe mid-point of the three lower sub-switches to the dual inverterdrive; the polarity inversion circuit has a first state and a secondstate: in the first state, the first and second master control switchesare controlled to be off and the first and second phase switch networkare not active; in the second state, the first and second master controlswitches are controlled to be on and the first and second phase switchnetwork are active.

In this variant, in the first state, power is directed to the vehicle;and in the second state, power is directed to the AC grid. The firstthree phase switch network can be coupled to the negative VSC1 DCterminal, and the second three phase switch network can be coupled tothe positive VSC2 DC terminal. In a further variation, the first threephase switch network is coupled to the negative VSC2 DC terminal, andthe second three phase switch network is coupled to the positive VSC1 DCterminal.

In another embodiment, a controller is provided that is configured tointerleave the gating signals to the switches of the three or morephases of the first voltage source converter and to interleave thegating signals to the switches of the three or more phases of the secondvoltage source converter which can reduce the peak current ripple intothe first or the second energy storages.

In another embodiment, a controller is configured to interleave thegating signals of the first and second voltage source converter switcheswhich are coupled to the same motor winding; resulting in reduced peakcurrent ripple in winding currents.

In another embodiment, a controller is configured to ensure the motorwinding currents are DC and each of the motor winding currents are ofequal DC value; resulting in no torque production in the open woundmotor.

In another embodiment, a controller is configured to deliver differentpower to the first energy storage and the second energy storage such aswhen the two energy storage devices are at different voltages, thecontroller configured to provide the different power by adjusting arelative duty cycle of the upper switches of the first VSC with respectto a duty cycle of the lower switches of the second VSC.

Corresponding methods, processes, controller circuits (e.g., gatecontrol circuits) and non-transitory machine readable media (storinginstruction sets, which when executed by a processor, cause theprocessor to perform steps of a method) are contemplated. Thenon-transitory machine readable media can also store gate controlsequences, which when transmitted to the switches, causes correspondingoperation of the switches.

An electric or hybrid electric vehicle is contemplated whichincorporates the powertrain descried in various embodiments. Similarly,a stand-alone CSC configured to couple to the other powertraincomponents is also contemplated, as well as a standalone power inversioncircuit that is configured to couple to the other powertrain components(such as a CSC).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a conventional current source converter in which theDC-link consists of an inductor and back emf source.

FIG. 2 is a high-level block diagram of some embodiments. The topologyincludes the following elements (from left to right): an optionalinterface power transformer, an input AC filter, a current sourceconverter front-end, an optional polarity inversion module for reversingthe power direction, two independent energy storage elements and adual-inverter drive in which motor is in open-winding configuration.

FIG. 3 is a more detailed representation of FIG. 2; where the currentsource converter, polarity inversion module, open-winding motor anddrive inverters have been presented in more detail.

FIG. 4 presents an embodiment of the polarity inversion module.

FIG. 5 presents a second embodiment of the polarity inversion module.

FIG. 6 presents a third embodiment of the polarity inversion module.

FIG. 7 presents a fourth and preferred embodiment of the polarityinversion module.

FIG. 8 presents a more specific embodiment of the embodiment presentedin FIG. 3.

FIG. 9 is an example polarity inversion module, according to someembodiments.

FIG. 10 is another example polarity inversion module, according to someembodiments.

FIG. 11 is an example embodiment of the polarity inversion module, FIG.9, according to some embodiments.

FIG. 12 presents a high-level diagram of the electrical inputs, controlinputs and outputs of the three-port electric powertrain for chargingand vehicle-to-grid mode. Describes at a high level, here are thecontrol inputs, here are the outputs.

FIG. 13 presents an embodiment which details one possible implementationof the preferred embodiment.

FIG. 14 presents a model of the DC-side of the integrated charger duringcharging mode.

FIG. 15 presents simulation results for Case 1. In Case 1, the vehicleis charged at 60 kW at unity power factor from a 600 V three-phase ACgrid, according to some embodiments. The energy storage elements have aterminal voltage of 300 V, respectively.

FIG. 16 presents simulation results for Case 2, according to someembodiments. In Case 2, the vehicle is charged at 60 kW at unity powerfactor from a 600 V three-phase grid. The energy storage elements are at325 V and 300 V, respectively. During steady-state, energy storageelement 2 is at a lower state of charge and is kept in the circuit, bysetting the duty ratio at 1. Energy storage element 1 is at the higherstate of charge and is modulated such that equal power is delivered toenergy storage elements 1 and 2.

FIG. 17 presents simulation results for Case 3, according to someembodiments. In Case 3, the vehicle is charged at 70 kW at a powerfactor of 0.95 lagging from a 600 V three-phase AC grid. The energystorage elements are each at 450 V.

FIG. 18 presents simulation results for Case 4, according to someembodiments. In Case 4, the vehicle is charged at 70 kW at a powerfactor of 0.95 leading from a 600 V three-phase AC grid. The energystorage elements are each at 450 V.

FIG. 19 presents simulation results for Case 5, according to someembodiments. In Case 5, the vehicle is charged at 70 kW at unity powerfactor from a 600 V three-phase grid. The energy storage elements areeach at 450 V.

FIG. 20 presents simulation results for Case 6, according to someembodiments. In Case 6, the vehicle is delivering 70 kW of power to the600 V three-phase grid at unity power factor. The energy storageelements are at 450 V.

FIG. 21 presents simulation results for Case 7, according to someembodiments. In Case 7 the vehicle is delivering 70 kW of power to the600 V three-phase grid at unity power factor. The energy storageelements are at 300 V.

FIG. 22 presents a variation for single-phase AC grid chargingapplications, according to some embodiments.

FIG. 23 presents a variation without bi-directional power capability,according to some embodiments.

FIG. 24 is a method diagram of a method for operating an integratedthree-phase ac charger for vehicle applications with dual-inverterdrive, according to some embodiments.

FIG. 25 is a computing device diagram of an example computing devicethat can be used for controlling gating to implement a method foroperating an integrated three-phase ac charger for vehicle applicationswith dual-inverter drive, according to some embodiments.

DETAILED DESCRIPTION

Electric or hybrid-electric vehicles are desirable relative toconventional combustion engine vehicles due to reductions in harmfulemissions. Combustion engines that utilize petrol or diesel can emittons of carbon dioxide among other harmful emissions, such as methane,nitrous oxide that potentially contribute to climate change. Electrichybrid engines can be adapted to use potentially both gasoline/dieseland electric power stored therein.

Electrical grid charging from DC sources is a simpler approach relativeto charging by AC grid infrastructure, but not always available. AC gridinfrastructure is more readily available but conversion approaches havetypically required expensive or cumbersome infrastructure elements forAC/DC conversion prior to use with an electric vehicle or a hybridelectric vehicle. For example, a AC/DC conversion stage can be conductedby an additional rectifier circuit, which, in certain situations,utilize magnetic components to improve efficiency of power flow/energytransfer.

An example of AC grid infrastructure for charging can includesupercharger stations, where a number of stalls are available forelectric or hybrid electric vehicles to park, and to plug in a cable tocharge. These supercharger stations are not as well distributed asconventional gasoline pumps for combustion engine vehicles, and canseverely limit viability of electric or hybrid electric vehicles as theoperating range of the electric or hybrid electric vehicles is typicallyless than that of a combustion engine vehicle having a full tank ofgasoline or diesel.

An AC/DC conversion stage adds infrastructure complexity (e.g., ifrequired at every AC grid interface at electric car charging stations),and the magnetic components (e.g., inductors, capacitors) are bothcumbersome (e.g., these components take up limited space at chargingstations and are heavy) and expensive (e.g., additional inductors can beespecially expensive). Electric vehicle adoption is limited by sparseavailability of electric vehicle charging stations, as the cost andspace requirements (e.g., limiting the number of stalls) for currentelectric car charging stations are high. Large distances betweenelectric car charging stations or queuing due to less stalls than anumber of vehicles to be charged can severely impact the viability ofelectric cars as electric vehicles only have limited range.

FIG. 1 presents a conventional current source converter 100 in which theDC link consists of an inductor and a back emf source. With thistopology it is possible to charge an energy storage element, such as abattery, from a three-phase AC-grid.

A drawback to this solution when considering for electric vehicle (EV)applications, is that an external power inductor, L_(dc) 102, isrequired adding significant cost, volume and weight to the charger. Inaddition, this topology does not address how to reverse the polarity ofthe emf source which is required for reversing the direction of power asrequired for V2G operating mode.

In Y. Han, M. Ranjram, and P. W. Lehn, “A bidirectional multi-port dc-dcconverter with reduced filter requirements,” in 2015 IEEE 16th workshopon control and modeling for power electronics (compel), 2015, pp. 1-6[Han], a three-port DC/DC converter structure is described which allowsfor power exchange between three independent DC ports. For EVapplications, this structure could be employed for managing powerbetween a DC-link and two independent energy storage sources.

In R. Shi, S. Semsar, and P. W. Lehn, “Constant current fast charging ofelectric vehicles via a dc grid using a dual-inverter drive,” IEEETransactions on Industrial Electronics, vol. 64, no. 9, pp. 6940-6949,Sep. 2017, an electric powertrain with integrated charging is described.This topology employs the structure in Han but with the integration ofthe powertrain components of the EV. The topology allows for faston-board charging without additional magnetics. However, the charger islimited to DC grid charging applications and does not feature buck-boostcharging capability. Therefore, a gap exists for integrated powertrainsolutions for three-phase AC grid charging with buck-boost capabilitythat re-utilize existing powertrain components to reduce weight, volume,and cost to the vehicle.

Accordingly, an improved approach for charging from an AC grid (e.g., amulti-phase AC grid) is desirable. The proposed approach is an improvedcircuit topology (and corresponding circuits, methods, and machineinstruction sets stored on non-transitory machine readable media) thatis directed to an environmental (green) technology that could help toresolve or mitigate environmental impacts by improving the viability ofelectric or hybrid vehicles. As the viability of electric or hybridvehicles is improved, reliance on combustion engines can be reduced tohelp conserve natural environment and oil/gas resources.

The main elements of a preferred embodiment are presented in FIG. 2. Themagnetic components of the electric motor, when not in use, can beleveraged for AC/DC conversion. Other embodiments are also contemplated.

The term module may be utilized in this description, and can include, invarious embodiments, physical electrical circuits that include physicalcomponents, such as interface terminals, electrical pathways (e.g.,wires), electrical nodes, resistors, semiconductors, switches, energystorage elements, reactive power elements, among others.

As shown in FIG. 2 at block schematic 200, an AC grid 202 and anoptional transformer 204 connect to an on-board powertrain through inputfilter 206. The on-board powertrain includes a current source converter208, and an optional polarity inversion module 210, which connects totwo energy storage elements 212A, 212B that connect to a motor 216through one voltage source converter each 214A, 214B.

The current source converter 208 is a circuit that operates as an AC/DCconversion stage and couples to a dual inverter drive system that hastwo charging stages (e.g., an upper charging stage and a lower chargingstage) that is connected across the motor 216 (e.g., across motorwindings). Because the dual inverter drive system connects through themotor 216 itself, the magnetics components of the motor are used for theAC/DC conversion, providing a potentially less cumbersome and lessexpensive approach to AC/DC conversion. Each of these stages has anenergy storage and voltage source converter.

For example, the upper charging stage has a first energy storage and afirst voltage source converter (VSC1). The lower charging stage has asecond energy storage and a second voltage source converter (VSC2). Thedual inverter drive can be configured to provide voltage boostingcapability, enabling power to be exchanged between the AC grid and thefirst or second energy storage elements (equivalently termed energystorages) when a sum of the energy storage voltages is greater than themaximum average rectified voltage across the CSC DC terminals.

Note, in this disclosure traction inverter 1 is used interchangeablywith voltage source converter 1 or VSC1.

Note, in this disclosure traction inverter 2 is used interchangeablywith the terms voltage source converter 2 or VSC2.

The motor 216 can be an open wound motor (e.g., the motor that can beused for locomotion) that is coupled between the first voltage sourceconverter and the second voltage source converter, and the open woundmotor has three or more motor windings. Each of these windings arecoupled to a corresponding AC terminal of each of the first voltagesource converter and the second voltage source converter.

An embodiment is detailed in FIG. 3, shown as circuit diagram 300. Fourdistinct embodiments of the polarity inversion module are presented inFIG. 4, FIG. 5, FIG. 6 and FIG. 7, shown in partial circuit diagrams400, 500, 600, and 700, respectively. FIG. 23 shows an embodiment wherethere is no polarity inversion module present.

The electric powertrain elements located on-board the vehicle are shownin FIG. 3. The electric powertrain circuit, in some embodiments, isprovided as a component of the electric or hybrid vehicle and can, forexample, reside on or within the electric or hybrid vehicle (e.g., as acircuit that is directly coupled to the motor and energy storagedevices) such that the electric or hybrid vehicle can connect directlyto three phase AC grid interfaces, even if the AC grid interface doesnot have an available AC/DC conversion stage, for example, when theelectric or hybrid vehicle's motor is not being used for locomotion. Anadditional controller circuit can be provided that is configured totoggle operation of the open wound motor between a locomotion state anda energy flow state. For example, the chassis of the electric or hybridvehicle can be used as a housing for the The electric powertraincircuit.

The on-board elements consist of a three-phase AC input filter 302, athree-phase CSC 304, a polarity inversion module 306, two energy storageelements 308, 310, and a dual-inverter drive 312. The dual inverterdrive features two voltage source converters and an open wound motor.

First, the main elements of an embodiment are described. This isfollowed by a description of a means of operating various embodiments.Finally, simulation cases are presented which demonstrate the operationof the electric powertrain for a range of representative operatingpoints.

Interface to Three Phase or Single Phase AC Grid

The electric powertrain can be charged and provide V2G services to boththree-phase AC and single-phase AC grids, in accordance with variousembodiments (not all embodiments necessarily provide V2G services).Uni-directional charging from the AC grid to the electric or hybridvehicle is contemplated in some embodiments. Alternatively,uni-directional charging to the AC grid from the electric or hybridvehicle is also contemplated in other embodiments.

A transformer between the vehicle and the AC grid may be requireddepending on local regulations regarding isolation and/or whetherstep-down or step-up of the AC grid connection voltage is required.

In this document, the term “AC grid” is used to refer to some general ACnetwork. Therefore, in this context AC grid is not restricted to beingjust an electrical grid but also encompasses other types of AC networkconnections. V2G charging is useful, for example, in emergencysituations, or situations where the grid is isolated and remote (e.g., arural grid). Depending on grid energy prices, it may also beeconomically advantageous to provide energy to the grid.

Three Phase Input Filter

The three-phase AC input filter 302 is located between the AC-grid andthe current source converter 304. The role of the input filter 302 is toattenuate the current harmonics generated by the current sourceconverter front-end from entering into the AC grid. This attenuation isgenerally required in order to comply with local harmonic standardswhile operating the device in either charging or V2G mode. The inputfilter 302 can be realized in multiple ways including being either ofpassive or active type. Additionally, the input filter 302 can belocated off the vehicle and/or it can be located between the AC-grid andthe transformer rather than being between the transformer and thevehicle as is presented in FIG. 3.

Current Source Converter Front-End

The current source converter (CSC) 304 has a positive and negative DCterminal; wherein the positive and negative DC terminal are interfacedto the positive DC terminal of the first VSC 314 and the negative DCterminal of the second VSC 316.

The three AC terminals of the CSC are interfaced to the AC networkthrough an optional input filter which provides filtering of harmonics.

The current source converter front-end (CSC) 304 functions by convertingthe line-side voltages across the low-pass AC filter into a voltage witha DC-component on the DC-side of the CSC. This conversion is realizedthrough gating of the switches of the CSC 304.

This DC-side voltage drives a uni-directional current with aDC-component on the DC-side of the CSC 304. The gating of the switches,which generates the DC-side voltage, converts the three-phase AC-sidecurrents into a DC-side current. The control of the gating signalsallows the CSC 304 to control for quantities such as the real power andreactive power exchanged with the AC-grid when in charging mode or V2Gmode, for instance.

The CSC 304 is also inherently fault tolerant ensuring the energystorage elements are protected in the event of an AC grid fault.

The CSC 304 includes a first circuit leg, a second circuit leg, and athird circuit leg. Each circuit leg corresponds to a corresponding CSCAC phase terminal of the three CSC AC phase terminals, and has at leastone upper switch and one lower switch. The upper switches are eachcoupled to a corresponding CSC AC phase terminal and the positive CSC DCterminal. The lower switches are each coupled to a corresponding CSC ACphase terminal and the negative CSC DC terminal.

Each of the upper and lower switches are controlled by gate controlsignals, which when only one upper switch is in an on-state, that switchwill conduct a current equal to the sum of the three winding currents,and when only one lower switch is operated, that switch will conduct acurrent equal to the sum of the three winding currents. These gatecontrol signals control the energy flow between the AC grid and theelectric vehicle/hybrid electric vehicle, exploiting the inductance ofthe motor to enable operation.

The powertrain components provide a variable back emf and a seriesinductance to the CSC. The upper and the lower switches of the CSC canbe configured in some embodiments such that both the real power andreactive power exchanged with the AC grid are separately controlled. TheCSC can provide voltage bucking capability, enabling power to beexchanged between the AC grid and the first or second energy storageswhen the sum of the energy storage voltages is less than the maximumaverage rectified voltage across the CSC DC terminals.

The two independent energy storage elements connected on either side ofthe motor via inverters can be electrically in series for charging andvehicle-to-grid mode. The ability to series connect the emfs is highlyadvantageous as the powertrain can realize higher dc-link voltagesresulting in improved overall efficiency and increased charging powercapability. Another advantage to the use of a CSC for the front-end isthat due to the inherent bi-directional blocking capability of theswitches of the CSC, the charging currents for the energy storageelements are controllable irrespective of state of charge and nominalenergy storage element voltages. The CSC can also feature fault-blockingcapability, which ensures the energy storage elements are protected inthe event of an AC grid fault (e.g., AC short circuit). The AC grid canbe optionally coupled to the CSC through an input filter, the inputfilter configured to filter out harmonic currents generated by theelectric powertrain from entering into the AC grid.

The structure of a CSC 304 front-end together with a variable back emfprovided by the differentially connected dual-inverter drive allows forbuck-boost operation for charging which is also highly advantageous. Inbuck-mode, the CSC front-end steps down the grid voltage; and inboost-mode, the dual-inverter drive steps-up the grid voltage.

In an example embodiment, the CSC 304 consists of 6 switches labeled inFIG. 3 as S_(a1), S_(a2), S_(b1), S_(b2), S_(c1) and S_(c2).

Each leg of the CSC 304 contains two switches—one in the upper arm andone in the lower arm of the leg. An arm is defined as the path between aDC terminal and an AC phase terminal. A leg or CSC phase is defined asthe path between the two DC-terminals of the CSC (i.e. between CSCp andCSCn).

In an example embodiment, each switch can require bi-polar voltageblocking capability and uni-directional current conduction capability. Acombination of both active and passive semiconductor switches can beused to realize the CSC 304 in the preferred embodiment.

When the switches of the CSC feature bipolar voltage blocking capabilityenabling both the real power and reactive power exchanged with the ACgrid to be separately controlled.

The CSC provides voltage bucking capability. This enables power to beexchanged between the grid and the energy storage elements when the sumof the energy storage element voltages is less than the maximum averagerectified voltage across the CSC DC terminals.

The DC link current of the CSC is unidirectional in both charging andV2G mode in some embodiments. In an embodiment of the device with thepolarity inversion module of FIG. 7, the DC link current during chargingmode is the current that flows from the CSCp terminal to the CSCnterminal.

In an embodiment embodiment of the device with the polarity inversionmodule 700 of FIG. 7, the DC link current during V2G mode is the currentthat flows from the ES1 n terminal to the ES2 p terminal. In thepolarity inversion module 400, 500, 600 of FIG. 4, FIG. 5 and FIG. 6,the DC link current during charging mode and discharge mode is thecurrent that flows from CSCp terminal to the CSCn terminal.

If only one upper and one lower CSC switch are active then the currentflowing into the upper switch will be equal to the DC link current andthe current flowing into the lower switch will be equal to the DC linkcurrent. The DC link current is equal to the sum of the motor windingcurrents. This can be mathematically expressed as follows,

i _(dc) =i _(w) +i _(v) +i _(u)

It is through controlling the states of the upper and lower switches ofthe CSC that the desired operation of the CSC is obtained.

In some embodiments of the current source converter there are 9 statesin which only one upper and one lower switch are active. These statesare summarized in the following Table along with the resulting phasecurrents i_(ta), i_(tb) and i_(tc) at the input of the CSC for each ofthe 9 CSC states.

State Number Active Switches I_(ta) I_(tb) I_(tc) 1 S_(a1) and S_(a2) 00 0 are active 2 S_(b1) and S_(b2) 0 0 0 are active 3 S_(c1) and S_(c2)0 0 0 are active 4 S_(a1) and S_(b2) i_(dc) −i_(dc) 0 are active 5S_(a1) and S_(c2) i_(dc) 0 −i_(dc) are active 6 S_(b1) and S_(a2)−i_(dc) i_(dc) 0 are active 7 S_(b1) and S_(c2) 0 i_(dc) −i_(dc) areactive 8 S_(c1) and S_(a2) −i_(dc) 0 i_(dc) are active 9 S_(c1) andS_(b2) 0 −i_(dc) i_(dc) are active

As can be observed in the above Table, under ideal conditions the phasecurrents at the input of the CSC have the possibility of three values,0, i_(dc) or −i_(dc) (where, i_(dc) is the dc link current) depending onthe states of the switches.

One approach for controlling the CSC is to use a space vector pulse withmodulation technique or SVPWM. This is only one such technique of manythat could be employed to control the CSC of some embodiments. With theSVPWM technique, in each switching period the CSC will undergo 3 of the9 states, each for a specified duration. In the following paragraphs,the SVPWM as applied to some embodiments are described. This is howeveronly one such control method and one such approach for implementing theSVPWM.

In this approach, it is the positive sequence component of the gridcurrent that is controlled. The positive sequence current reference is asinusoidal term which can be expressed as follows,

Ip=|Ip|cos(θ)

Where Ip is the grid reference current where |Ip| is the magnitude ofthe reference and θ is the phase angle of the grid reference current.There are many ways to determine the reference current depending on thecontrol objectives. For example, if it is desired to draw a certain realand reactive power from the grid, Ip can be approximated as follows,

Ip=(P+jQ)*/sqrt(3)/Vg+*

Where, “*” denotes a complex conjugate and Vg+ is the positive sequencegrid voltage component.

It is however convenient to re-express the reference current in terms ofa modulation index and a phase angle. The result is as follows,

m _(i) =|Ip|/I _(dc)

θ=θ_(v)+θ_(ref)

Note, in some embodiments m_(i) ranges from approximately 0 to 1 and θranges from approximately −180 to +180 degrees or equivalently 0 to 360degrees.

There are different approaches to measure the positive sequence gridvoltage phase angle, θ_(v). An example of one such approach is to use aphase lock loop (PLL).

The CSC undergoes three states per switching period. The set of threestates that the CSC undergoes depends on the current reference angle, θ.There are a total of 6 different sets of the three states. The range ofθ values in which the CSC features the same three states over aswitching period are termed zones in this disclosure.

The zones and the corresponding CSC states are summarized in the belowtable,

Zone (z) θ (degrees) State i State ii State iii 0 −30 to +30 4 5 1 1  30to +90 5 7 3 2  90 to 150 7 6 2 3 150 to 210 6 8 1 4 210 to 270 8 9 3 5270 to −30 9 4 2

Where, state i, ii and iii denote the three states of the CSC for thatparticular zone. The states being defined in a previous Table. Forinstance, the 3 states corresponding to zone 4 are states 8, 9 and 3.The dwell times for states i, ii and iii (Ti, Tii and Tiii,respectively) can be approximated by the following formulae,

T _(i) =m _(i)*sin(30 deg−(θ−z*60))=

T _(ii) =m _(i)*sin(30 deg+(θ−z*60))

T _(iii)=1−T _(i) −T _(ii)

Where, z denotes a particular zone.

To cause three different converter states per switching period, 5 uniquegating signals are employed in some embodiments which are distributed tothe 6 switches of the CSC.

The 5 unique gating signals are described in the following table:

Low State Interval High State Interval G1 t = T_(i) to T_(s) t = 0 toT_(i) G2 t = 0 to T_(i) and t = T_(i) + T_(ii) t = T_(i) to T_(i) +T_(ii) G3 t = 0 to T_(i) + T_(ii) t = T_(i) + T_(ii) to T_(s) G4 t = 0to T_(s) — G5 — t = 0 to T_(s) Note, t = 0 denotes the start of aswitching period; and t = Ts denotes the end of a switching period.

Where, for instance, G1 corresponds to a low value (or equivalently offstate) from t=T_(i) to T_(s); and G1 corresponds to a high value (orequivalently on state) from t=0 to T_(i). Note, T_(s) denotes aswitching period.

The 5 gating signals are distributed to the CSC switches depending onthe zone of operation. The distribution of the gating signals withrespect to the zone of operation is summarized by the following Table,

Gating Signal Zone G1 G2 G3 G4 G5 0 S_(b2) S_(c2) S_(a2) S_(a1) S_(b1),S_(c1) 1 S_(a1) S_(b1) S_(c1) S_(c2) S_(a2), S_(b2) 2 S_(c2) S_(a2)S_(b2) S_(b1) S_(a1), S_(c1) 3 S_(b1) S_(c1) S_(a1) S_(a2) S_(c2),S_(b2) 4 S_(a2) S_(b2) S_(c2) S_(c1) S_(a1), S_(b1) 5 S_(c1) S_(a1)S_(b1) S_(b2) S_(c2), S_(a2)

Note the above is only one such example of an implementation of thecontrol for the CSC and so other types of control would also beapplicable.

It is the CSC that performs the bucking for this converter. Bucking isrequired in some embodiments, particularly in cases where the maximumaverage rectified voltage across the CSC DC terminals is greater thanthe total sum of the energy storage element 1 and energy storage element2 voltages. Bucking in some embodiments is performed through adjustingthe modulation index, mi.

By adjusting the modulation index, mi, the power delivered to the energystorage elements can be controlled in this case. By reducing themodulation index the power to the energy storage elements is reduced andby increasing the modulation index the power to the energy storageelements is increased in this case. The following is an approximateexpression for the dc link current,

I _(dc)=(√{square root over (3/2V)}_(s,rms) m _(i) cos(θ)−V _(d))/R

where, R is an equivalent resistance of the dc circuit and Vd is theback emf voltage provided by the dual-inverter drive.

Therefore, by reducing mi the dc link current, I_(dc), will decrease. Inbuck mode, by maximizing Vd the dc link current is minimized for a fixedamount of power to be delivered to the vehicle, for instance.

Therefore in some embodiments, it is desired to maximize the back emfvoltage of the dual inverter drive during buck mode charging. Thereforeif V_(d) is relatively fixed during buck mode, it is by adjusting themodulation index mi that the power to be exchanged can be controlled.Note, the θ term also impacts the dc link current but its effect is, insome embodiments, is less than the modulation index term.

It should be noted, that in V2G mode, for a given reactive power, Q,delivered to the AC grid, the phase of the string currents will be phaseshifted by 180 degrees in some embodiments. This phase shifting by 180degrees can be performed in some embodiments by adjusting the thetaterm, θ_(ref).

Also as noted before, the positive sequence grid current reference,Ip=|Ip|cos(θ_(r)), has a phase angle term, θ. By adjusting θ it ispossible to adjust the reactive power delivered into the grid, Q. Note,Ip is related to related to Q by the following expression,

Ip=(P+jQ)*/sqrt(3)/Vg+*

By adjusting θ_(r) it is possible to adjust the value of Q.

Dual-Inverter Drive and Polarity Inversion Module

The charger is switched between charging and vehicle-to-grid modethrough use of a polarity inversion circuit (e.g., polarity inversionmodule 306) between the CSC and the dual-inverter drive.

The role of the polarity inversion module 306 is to invert the polarityof the DC-side back emf generated by the dual-inverter drive. Note, thepolarity inversion module 306 is optional, and included only in someembodiments.

The polarity inversion module 306 can be coupled between the CSC and theupper charging stage and the lower charging stage such that the thepolarity inversion module 306 is coupled to the CSC at the positive CSCDC terminal and the negative CSC DC terminal, and the polarity inversionmodule 306 is coupled to the upper charging stage at the positive VSC1DC terminal, and coupled to the lower charging stage at a negative VSC2DC terminal.

The CSC requires a back emf and a series inductance. The polarityinversion module 306 is configured to invert a polarity of a back emfprovided by the dual inverter drive such that the electric vehicle orthe hybrid-electric vehicle is able to provide power to the AC grid.

The back emf in conjunction with the rectified voltage of the CSC, setsthe DC-side current. The series inductance attenuates the DC-sidecurrent ripple. The dual-inverter drive already on the vehicle providesthis back emf and series inductance. The dual-inverter drive as seen inFIG. 3 consists of an open-winding motor 312 and two voltage sourceconverters or inverters (voltage source converters are used in thisdocument interchangeably with the term inverters) where each motorwinding is differentially connected to the two inverters. Connectedacross the DC terminals of each inverter is an energy storage element308 310.

The two voltage source converters (VSCs) have three or more phases;wherein each phase has an associated AC terminal; and each VSC has apositive and negative DC terminal which couple the VSC to one or moreenergy storage elements, i.e. traction inverter 1 to ES1 308 andtraction inverter 2 to ES2 310.

The open-wound motor has three or more motor windings; wherein each ofthe motor winding has two terminals; wherein one motor winding terminalis interfaced to an AC terminal of a first VSC 314 and the second motorwinding terminal is interfaced to an AC terminal of a second VSC 316. Inthis configuration, each of the motor windings is connected to one phaseof the two inverters. The motor windings can each be modelled asinductors in this configuration. The inductance value is due to theleakage inductance of each of the motor windings in some embodiments.Therefore, there is a leakage inductance between the AC terminal of thefirst VSC and the AC terminal of the second VSC which are coupled to thesame motor winding. For charging and V2G, this leakage inductance is asufficient inductance in some embodiments such that no additionalexternal inductance is required to be added to the powertrain.

The dual inverter drive provides voltage boosting capability. Thisenables power to be exchanged between the AC network and the energystorage elements when the sum of the energy storage element voltages isgreater than the maximum average rectified voltage across the CSC DCterminals.

The polarity inversion module 306 interfaces the DC-terminals of theinverter to the DC-terminals of the CSC 304. The polarity inversionmodule 306 is configured such that the back emf provided by the twoinverters 314 316 are of the same polarity for charging and V2G mode.

The polarity inversion module 306 enables a mode change between chargingmode and V2G mode by inverting the polarity of the back emf provided bythe dual-inverter drive, in an embodiment.

Therefore the CSC is coupled to the VSCs through a polarity inversionmodule enabling V2G operation. Note, if V2G operation is not requiredthen the polarity inversion module can be omitted.

Description of Upper and Lower Charging Stage Elements

In an embodiment, the two inverters 314316 of the charging stages eachconsist of 6 switches, 3 upper switches and 3 lower switches. Note that,the motor can have three phases, in some examples. Each of the switchesrequires bi-directional current conduction capability and uni-polarvoltage blocking capability. An example implementation is IGBTs withanti-parallel diodes.

As can be observed in FIG. 3, both the energy storage elements as wellas the polarity inversion module are connected in parallel to the DCcapacitors of the inverters 314 316. The energy storage elements areindependent and can be of different type and state-of-charge (or of thesame).

For instance, energy storage element 1 308 can be of a battery type andenergy storage element 2 310 can be of super-capacitor type. Thisflexibility allows for incorporation of higher power density elementsfor use in traction mode without an additional power electronic stage,for instance.

The gating of the upper and lower switches of the traction inverters arecomplementary in some embodiments. For example, when the upper switchfor phase “w” is on in traction inverter 1 the lower switch for phase“w” is off in traction inverter 1.

Due to the differential connection of the dual inverter drive, the threephases of the traction inverter can be modelled as three separatebranches as illustrated in diagram 1400 of FIG. 14. Each branchcorresponds to one of the three phases of the dual-inverter drive insome embodiments, i.e., phase w, v and u.

In an embodiment, in charging mode, when the upper switch of the uppercharging stage for phase “w” is on (or equivalently conducting oractive), the ES1 is by-passed in that branch. Conversely, when the lowerswitch of the upper charging stage for phase “w” is on, the ES1 isinserted in that branch.

The principle applies to the other phases “v” and “u”. Conversely, incharging mode when the upper switch of the lower charging stage forphase “w” is on (or equivalently conducting or active), the ES2 isinserted in that branch. And when the lower switch of the lower chargingstage for phase “w” is, the ES2 is by-passed in that branch. Theprinciple applies to the other phases “v” and “u”.

In V2G mode, in an example embodiment of the polarity inversion module1100 of FIG. 11, when the upper switch of the upper charging stage forphase “w” is on (or equivalently conducting or active), the ES1 isinserted in that branch. And when lower switch of the upper chargingstage for phase “w” is, the ES1 is by-passed in that branch. Theprinciple applies to the other phases “v” and “u”. Conversely, in V2Gmode, in an example embodiment of the polarity inversion module of FIG.11, when the upper switch of the lower charging stage for phase “w” ison (or equivalently conducting or active), the ES2 is by-passed in thatbranch. And\ when lower switch of the lower charging stage for phase “w”is on, the ES2 is inserted in that branch. The principle applies to theother phases “v” and “u”

By decreasing the duration or duty cycle in a given switching periodthat ES1 or ES2 are inserted into a branch the average back emf of thatbranch will decrease. This ability to reduce the back emf voltageenables the dual inverter drive to perform a boosting function such thatpower can be exchanged when the sum of the ES1 and ES2 voltages isgreater than the maximum average rectified voltage across the CSC DCterminals.

When the energy storage element is inserted into the branch in someembodiments, that energy storage element will be charged during chargingmode and discharged during discharge mode by that branch current. Thatbranch current is the current of the motor winding for that branch.

Conversely, when the energy storage element is by-passed for aparticular branch, in some embodiments, that energy storage element willnot be charged or discharged by that branch current. Therefore, as anexample if ES1 was inserted in all three branches it would be charged incharge mode or discharged in discharge mode by all three motor windingcurrents.

Conversely, if ES1 was bypassed in all three branches it would not becharged or discharged by the branch current. Note, that the powerdelivered to or delivered by the energy storage element is dictated bythe voltage of the energy storage element and the current flowingthrough that energy storage element.

Therefore, when it is mentioned that the energy storage element would becharged or discharged by a particular current it means that the powerdelivered to or removed from the energy storage element is equal to thevoltage of the energy storage element multiplied by the current flowingthrough that energy storage element. If losses are not considered, thesum of the power to energy storage element 1 and energy storage element2 is the power exchanged with the AC grid in some embodiments.

Given the structure of the dual-inverter drive, it is possible todeliver a different power to ES1 and ES2. If in a particular branch, ES1is inserted for a greater duration in a given switching period then ES2,the motor winding current for that branch will flow into ES1 for moreduration than ES2. If ES1 and ES2 have approximately the same voltagevalue, then the power into ES1 will be greater than the power into ES2.The power into ES1 and into ES2 for a particular phase, can beapproximated by the following equation,

P _(ES1,w) =d _(w1) *E _(s1)

P _(ES2,w) =d _(w2) *E _(s2)

Therefore, by adjusting the duty cycle d_(w1) with respect to dw2 it ispossible to deliver differential power to ES1 with respect to ES2. Thesame principle applies for the other traction inverter phases.

Description of Polarity Inversion Module Elements

The role of the polarity inversion module 306 is to invert the polarityof the back emf provided by the dual-inverter drive. Polarity inversionis required for enabling V2G capability.

Three variations of the polarity inversion module 306 are outlined inFIG. 4, FIG. 5, and FIG. 6. These variations are applicable to the CSCfront-end topology 304 depicted in FIG. 3. The fourth variation of thepolarity inversion module is presented in FIG. 7. This fourth variationis applicable to the subset of CSC topologies which share the structureof that presented in diagram 800 of FIG. 8. In this CSC structure, themid-point of each switch pair for each arm is accessible to the polarityinversion module 306.

Polarity Inversion Module Variant 1

The first embodiment of the polarity inversion module is outlined inFIG. 4.

In this variant, the polarity inversion circuit is coupled to the uppercharging stage at the negative VSC1 DC terminal and to the lowercharging stage at a positive VSC2 DC terminal, and includes at least oneswitch and that interfaces the CSC with the dual inverter drive, withthe polarity inversion circuit having a first state and a second state;the first state coupling the positive CSC DC terminal and the positiveVSC1 DC terminal, and coupling the negative CSC DC terminal and thenegative VSC2 DC terminal; and a second state coupling the positive CSCDC terminal and the negative VSC1 DC terminal, and coupling the negativeCSC DC terminal and the positive VSC2 DC terminal; wherein the in thefirst state, power is directed to the electrical vehicle or the hybridelectric vehicle and the in the second state, power is directed to theAC grid.

An example mechanical switch solution is shown at 400. In thisembodiment, there is a double-pole double-throw switch (DPDT)interfacing the CSC with the dual-inverter drive. There are two switchstates for the DPDT switch.

The can be adapted to first state and a second state; the first statecoupling the positive CSC DC terminal and the positive VSC1 DC terminal,and coupling the negative CSC DC terminal and the negative VSC2 DCterminal; and a second state coupling the positive CSC DC terminal andthe negative VSC2 DC terminal, and coupling the negative CSC DC terminaland the positive VSC1 DC terminal; wherein the in the first state, poweris directed to the vehicle and the in the second state, power isdirected to the grid.

Referring to FIG. 4, in switch state 1, the CSCp and ES1 p terminals areconnected; and the CSCn and the ES2 n terminals are connected. In switchstate 2, the CSCp and ES1 n terminals are connected; and the CSCn andES2 p terminals are connected. Please note that there are alternateswitch state possibilities that will allow for inverting the back emfvoltage. The presented case was only one such example.

Note in the first switch position, the positive dc terminal of the CSCis connected to the positive dc terminal of the first VSC and thenegative dc terminal of the CSC is connected to the negative terminal ofthe second VSC; and the second switch position, the positive dc terminalof the CSC is connected to the negative dc terminal of the first VSC andthe negative dc terminal of the CSC is connected to the positiveterminal of the second VSC.

Not it is also possible for the second position to be such that thepositive dc terminal of the CSC is connected to the negative terminal ofthe second VSC and the negative dc terminal of the CSC is connected tothe positive dc terminal of the first VSC.

Additionally, while the mechanical switch solution shown at 400 is of aDPDT switch it would also be possible to implement this with a DPSTswitch.

As described in an earlier section, depending on the states of the uppertraction inverter switches either ES1 will be inserted or by-passed inthe traction inverter phase and depending on the states of the lowertraction inverter switches either ES2 will be inserted or by-passed inthe traction inverter phase (or equivalently termed branch).

For each of the polarity inversion module variants, the polarityinversion module has a first state and a second state. The currentflowing into ES1 and ES2 will be positive in the first state and in asecond state, the current flowing into ES1 and ES2 will be negative.

This ability to to reverse the direction of the current flowing into ES1and ES2 gives the polarity inversion module the ability to in effectreverse the polarity of ES1 and ES2.

Therefore, in the first state the back emf of the dual-inverter can bemodelled as a positive voltage value and in the second state the backemf of the dual-inverter can be modelled as a negative voltage value. Insome embodiments of the polarity inversion module variant 1, when ES1 pis coupled to CSCp and ES2 n is coupled to CSCn, the currents into ES1and ES2 are positive and conversely when CSCp is coupled to ES1 n andCSCN is coupled to ES2 p the currents into ES1 and ES2 are negative.

Note, there may be other ways to connect this polarity inversion modulevariant to the VSC DC terminals.

An advantage of this variant of the polarity inversion module is that itis a mechanical solution that may be easier than a semiconductor switchbased solution and cost effective to implement.

A limitation of this variant is that due to being a mechanical solution,the speed of switching between charge and discharge module is slower insome embodiments to a polarity inversion module in which semiconductorswitches are employed.

Polarity Inversion Module Variant 2

FIG. 5 presents an alternate embodiment of the polarity inversionmodule. The polarity inversion circuit could alternatively consist of atleast four semiconductor switches with each switch of the at least foursemiconductor switches coupling one CSC DC terminal to one VSC DCterminal.

The switches can each be realized either via mechanical switches and/orelectronic switches. A summary of the blocking voltage and currentconduction constraints are as follows:

Switch S _(pr1) : V _(pr1)>0 V,I _(pr1)<0 A

Switch S _(pr2) : V _(pr2)>0 V,I _(pr2)>0 A

Switch S _(pr3) : V _(pr3)>0 V,I _(pr3)>0 A

Switch S _(pr4) : V _(pr4)>0 V,I _(pr4)<0 A

One switch couples the positive dc terminal of the CSC to the positiveterminal of the first VSC; one switch couples the positive dc terminalof the CSC to the negative terminal of the second VSC; one switchcouples the negative dc terminal of the CSC to the positive terminal ofthe first VSC; one switch couples the negative dc terminal of the CSC tothe negative terminal of the second VSC.

Each switch must block a uni-polar voltage of positive polarity andconduct uni-directional current. The direction of current is oppositefor the upper and lower switch of a phase. An example implementation ofthis embodiment of the polarity inversion module is presented in thepartial circuit diagram 900 of FIG. 9.

As described in an earlier section, depending on the states of the uppertraction inverter switches either ES1 will be inserted or by-passed inthe traction inverter phase and depending on the states of the lowertraction inverter switches either ES2 will be inserted or by-passed inthe traction inverter phase (or equivalently termed branch). For each ofthe polarity inversion module variants, the polarity inversion modulehas a first state and a second state.

The current flowing into ES1 and ES2 will be positive in the first stateand in a second state, the current flowing into ES1 and ES2 will benegative. This ability to to reverse the direction of the currentflowing into ES1 and ES2 gives the polarity inversion module the abilityto in effect reverse the polarity of ES1 and ES2.

Therefore, in the first state the back emf of the dual-inverter can bemodelled as a positive voltage value and in the second state the backemf of the dual-inverter can be modelled as a negative voltage value. Insome embodiments of the polarity inversion module variant 2, when ES1 pis coupled to CSCp and ES2 n is coupled to CSCn, the currents into ES1and ES2 are positive and conversely when CSCp is coupled to ES2 n andCSCn is coupled to ES1 p the currents into ES1 and ES2 are negative.

Note, there may be other ways to connect this polarity inversion modulevariant to the VSC DC terminals.

An advantage of this variant of the polarity inversion module is that itis a power electronic solution and therefore switching between chargeand discharge mode could be made quickly. Additionally, electricalconnections between the polarity inversion module and the upper andlower charge stage are only required in some embodiments on the ES1 pand ES2 n terminals. A limitation of this variant is that the blockingvoltage for the polarity inversion module switches is the sum of the ES1and ES2 voltages.

Polarity Inversion Module Variant 3

FIG. 6 presents an alternate embodiment of the polarity inversionmodule. The switches can each be realized either by mechanical switchesand/or electronic switches. A summary of the blocking voltage andcurrent conduction constraints are as follows:

Switch S _(pr1) : V _(pri)<0 V,I _(pr1)>0 A

Switch S _(pr2) : V _(pr2)>0 V,I _(pr2)>0 A

Switch S _(pr3) : V _(pr3)>0 V,I _(pr3)>0 A

Switch S _(pr4) : V _(pr4)<0 V,I _(pro)>0 A

One switch couples the positive dc terminal of the CSC to the positiveterminal of the first VSC; one switch couples the positive dc terminalof the CSC to the negative terminal of the first VSC; one switch couplesthe negative dc terminal of the CSC to the positive terminal of thesecond VSC; one switch couples the negative dc terminal of the CSC tothe negative terminal of the second VSC.

Each switch must block uni-polar voltages and conduct current ofpositive direction. An example implementation of this embodiment of thepolarity inversion module is presented in diagram 1000 of FIG. 10.

As described in an earlier section, depending on the states of the uppertraction inverter switches either ES1 will be inserted or by-passed inthe traction inverter phase and depending on the states of the lowertraction inverter switches either ES2 will be inserted or by-passed inthe traction inverter phase (or equivalently termed branch). For each ofthe polarity inversion module variants, the polarity inversion modulehas a first state and a second state.

The current flowing into ES1 and ES2 will be positive in the first stateand in a second state, the current flowing into ES1 and ES2 will benegative. This ability to to reverse the direction of the currentflowing into ES1 and ES2 gives the polarity inversion module the abilityto in effect reverse the polarity of ES1 and ES2.

Therefore, in the first state the back emf of the dual-inverter can bemodelled as a positive voltage value and in the second state the backemf of the dual-inverter can be modelled as a negative voltage value. Insome embodiments of the polarity inversion module variant 3, when ES1 pis coupled to CSCp and ES2 n is coupled to CSCn, the currents into ES1and ES2 are positive and conversely when CSCp is coupled to ES1 n andCSCn is coupled to ES2 p the currents into ES1 and ES2 are negative.

An advantage of this variant of the polarity inversion module is that itis a power electronic solution and therefore switching between chargeand discharge mode could be made quickly. Additionally, the blockingvoltage for the polarity inversion module switches is equal to eitherES1 or ES2 voltages, respectively. A disadvantage of this variant isthat the polarity inversion module connects to ES1 p, ES1 n, ES2 p andES2 n.

Note, there may be other ways to connect this polarity inversion modulevariant to the VSC DC terminals.

Polarity Inversion Module Variant 4

FIG. 7 presents an alternate embodiment of the polarity inversionmodule.

Each phase of the CSC is associated with two switches, an upper switchcorresponding to the phase and a lower switch corresponding to thephase, each of the upper switch and the lower switch corresponding tothe phase comprising a first and a second series connected sub-switcheswith an accessible mid-point.

The first sub-switch provides positive voltage blocking capability andthe second sub-switch provides negative voltage blocking capability.

The polarity inversion module includes a first three phase switchnetwork and a second three phase switch network, with each three phaseswitch network including at least four switches, three switches for eachphase and one master switch that is to controllable.

The positive CSC DC terminal and the positive VSC1 DC terminal areelectrically bonded, and the negative CSC DC terminal and the negativeVSC2 DC terminal are electrically bonded in this example.

The first three phase switch network couples the mid-point of the threeupper sub-switches to the dual inverter drive.

The second three phase switch network couples the mid-point of the threelower sub-switches to the dual inverter drive; the polarity inversioncircuit has a first state and a second state: in the first state, thefirst and second master control switches are controlled to be off andthe first and second phase switch network are not active; in the secondstate, the first and second master control switches are controlled to beon and the first and second phase switch network are active.

In the first state, power is directed to the vehicle; and in the secondstate, power is directed to the AC grid. The first three phase switchnetwork can be coupled to the negative VSC1 DC terminal, and the secondthree phase switch network can be coupled to the positive VSC2 DCterminal.

In a further variation, the first three phase switch network is coupledto the negative VSC2 DC terminal, and the second three phase switchnetwork is coupled to the positive VSC1 DC terminal.

As an example implementation using a number of switches, the polarityinversion module can include 8 switches, denoted as S_(pr1), S_(pr2), .. . , S_(pr8). Switch S_(pr1) must have the capability of blockingvoltages and conducting currents of the same polarity and direction,respectively, as that required of the corresponding phase switch,S_(a1). Switch S_(pr5) must have the capability of blocking voltages andconducting currents of the same polarity and direction as that requiredof the corresponding phase switch, S_(a4). Similar requirements apply tothe phase b switches (S_(pr2) and S_(pr6)) and phase c switches (S_(pr3)and S_(pr7)).

If S_(pr1), S_(pr2) and S_(pr3) are implemented with switches withreverse voltage blocking capability (such as IGBTs), S_(pr4) is notrequired and can instead be replaced by a conductive element. Similarly,if S_(pr5), S_(pr6) and S_(pr7) are implemented with switches withreverse voltage blocking capability, S_(pr8) is not required and caninstead be replaced by a conductive element. This polarity inversionmodule variant is configured such that either S_(a1), S_(b1), and S_(c1)are conducting or S_(pr1), S_(pr2), . . . , S_(pr4) are conducting.

The same principle applies to the lower arm switches. In an embodiment,in charging mode, the polarity inversion elements S_(pr1), S_(pr2), . .. S_(pr8) are non-conducting. In this mode, the positive terminal of theCSC is connected to the positive terminal of energy storage element 1;and the negative terminal of the CSC is connected to the negativeterminal of energy storage element 2.

In an example embodiment, in V2G mode, the polarity inversion elementsS_(pr1), S_(pr2), . . . , S_(pr8) are conducting. In this mode, the CSCmid-points, CSCp_a, CSCp_b and CSCp_c, are connected to the negativeterminal of energy storage element 1; and the CSC mid-points, CSCn_a,CSCn_b and CSCn_c, are connected to the positive terminal of energystorage element 2.

Note, the switches S_(pr4) and S_(pr8) can be implemented with either amechanical type-switch or semi-conductor type-switch.

An example implementation of this embodiment of the polarity inversionmodule is presented in diagram 1100 of FIG. 11.

Note, in this mode, each phase of the CSC features two switches, a firstswitch termed the upper switch and a second switch termed the lowerswitch. Each of the CSC switches is composed of two sub-switches, afirst sub-switch provides positive voltage blocking capability and asecond sub-switch provides negative voltage blocking capability.

A first, second and third switch interface the mid-point of the threeupper sub-switches of the CSC to a fourth switch. The fourth switch isinterfaced to the negative DC terminal of the first VSC.

A fifth, sixth and seventh switch interface the mid-point of the threeupper sub-switches of the CSC to an eighth switch. The eighth switch isinterfaced to the positive DC terminal of the second VSC.

As described in an earlier section, depending on the states of the uppertraction inverter switches either ES1 will be inserted or by-passed inthe traction inverter phase and depending on the states of the lowertraction inverter switches either ES2 will be inserted or by-passed inthe traction inverter phase (or equivalently termed branch).

For each of the polarity inversion module variants, the polarityinversion module has a first state and a second state. The currentflowing into ES1 and ES2 will be positive in the first state and in asecond state, the current flowing into ES1 and ES2 will be negative.This ability to to reverse the direction of the current flowing into ES1and ES2 gives the polarity inversion module the ability to in effectreverse the polarity of ES1 and ES2.

Therefore, in the first state the back emf of the dual-inverter can bemodelled as a positive voltage value and in the second state the backemf of the dual-inverter can be modelled as a negative voltage value. Insome embodiments of the polarity inversion module variant 4, when Spr4and Sp8 are off (i.e. phase switch networks are not conducting current),the currents into ES1 and ES2 are positive and conversely when Spr4 andSp8 are on (i.e. the phase switch networks are conducting current), thecurrents into ES1 and ES2 are negative.

Note, there may be other ways to connect this polarity inversion modulevariant to the VSC DC terminals.

An advantage of this variant over the other polarity inversion modulevariants is that the losses in charging mode should be comparable to thelosses in charging mode in electric power trains that do not feature anypolarity inversion module. This is because there are no additionalswitches inserted in the circuit during charge mode. Note, CSCp iselectrically bonded to ES1 p and CSCn is electrically bonded to ES2 n inthis variant. A limitation of this variant is that more switches arerequired.

Note, there may be other ways to connect this polarity inversion modulevariant to the VSC DC terminals.

Operating Mechanism Overview of Operating Mechanism

An overview of the operating mechanism during charging and V2G modes ofoperation is presented in FIG. 12 as shown in diagram 1200. As can beseen the inputs to the converter are: 1) three-phase AC grid voltage; 2)energy storage element 1 emf; and 3) energy storage element 2 emf. Thecontrolled quantities are the three-phase AC input current and thecharging currents to energy storage element 1 and 2. Therefore, thisconverter operates as a three-port converter unlike a conventionalcurrent source converter which operates as a two-port converter. Aconverter is a machine that can be used to implement the operatingmechanism and variants thereof.

Control of Integrated Powertrain for Charging

To illustrate the operation of the converter in charging mode it is bestto refer to an example implementation such as that presented in FIG. 13at circuit diagram 1300.

With the control one or more states of the one or more switches withinthe VSCs and the CSC are controlled to regulate the active power beingexchanged between the energy storage elements and the AC network.

In charging mode, the two active switches of the polarity inversionmodule 306 will not be conducting. In this configuration, the positiveterminal of energy storage element 1, ES1 p, will be connected to thepositive rail of the current source converter, CSCp; and the negativeterminal of the energy storage element 2, ES2 n, will be connected tothe negative rail of the current source converter, CSCn. Therefore, inthis mode a back emf of positive polarity is applied to the currentsource converter. If V2G operation is not required then the polarityinversion module may be entirely omitted.

During charging (and V2G) mode, the dual-inverter drive effectivelyconsists of three parallel branches; where, each branch consists of twoemf sources and a series inductance. The series inductance is theleakage inductance of the motor winding.

By alternatively gating the upper and lower switches of the uppercharging stage of a branch, energy storage element 1 is alternativelyby-passed and inserted into the branch, respectively in charging mode;and by gating the upper and lower switch of the lower charging stage,energy storage element 2 is alternatively inserted and by-passed in thebranch, respectively, in charging mode. Conversely in V2G mode, byalternatively gating the upper and lower switches of the upper chargingstage, energy storage element 1 is alternatively inserted and by-passedin the branch, respectively; and by gating the upper and lower switch ofthe lower charging stage, energy storage element 2 is alternativelyby-passed and inserted into the branch, respectively.

Therefore, by modulating the gating signals, each branch has twovariable emf sources—ranging from the full emf of the energy storageelement to 0 volts in the ideal case.

The above is illustrated in the circuit diagram 1400 of FIG. 14. Pleasenote, that the voltage sources of the circuit diagram in FIG. 14 aredrawn such that the polarity corresponds to charging mode.

For V2G mode, each voltage source in the circuit diagram of FIG. 14 willhave the opposite polarity. The variable emfs shown in FIG. 14 can bemathematically expressed as follows,

v _(u1) =v _(ES1) ·d _(u1)(1)

v _(v1) =v _(ES1) ·d _(v1)  (2)

v _(w1) =v _(ES1) ·d _(w1)  (3)

v _(u2) =v _(ES2) ·d _(u2)  (4)

v _(v2) =v _(ES2) ·d _(v2)  (5)

v _(w2) =v _(ES2) ·d _(w2)  (6)

where, d_(u1), . . . , d_(w2) denote duty ratios ranging from 0 to amaximum value of 1; v_(ES1) is the emf of energy storage element 1; andV_(ES2) is the emf of energy storage element 2. To avoid torquegeneration during charging, the DC currents for the three-phase windingsare controlled to be equal. Correspondingly, the DC current component ofthe three-winding currents is expressed as follows,

$\begin{matrix}{I_{v,{dc}} = {I_{w,{dc}} = {I_{u,{dc}} = \frac{I_{dc}}{3}}}} & (7)\end{matrix}$

Therefore, the average power to the two energy storage elements can becalculated as follows,

$\begin{matrix}{\mspace{79mu}{P_{ES1} = {\frac{I_{dc}}{3} \cdot \left( {{V_{ES1} \cdot d_{u1}} + {V_{ES1} \cdot d_{v1}} + {V_{ES1} \cdot d_{w1}}} \right)}}} & (8) \\{\mspace{79mu}{P_{ES2} = {\frac{I_{dc}}{3} \cdot \left( {{V_{ES2} \cdot d_{u2}} + {V_{ES2} \cdot d_{v2}} + {V_{ES2} \cdot d_{w2}}} \right)}}} & (9) \\{{{{If}\mspace{14mu} d_{u1}} = {d_{v1} = {d_{w1} = d_{1}}}},{{{and}\mspace{14mu} d_{u2}} = {d_{v2} = {d_{w2} = d_{2}}}},{then},{P_{ES1} = {I_{dc} \cdot V_{ES1} \cdot d_{1}}}} & (10) \\{\mspace{79mu}{P_{ES2} = {I_{dc} \cdot V_{ES2} \cdot d_{2}}}} & (11)\end{matrix}$

Therefore, the charging currents for the two energy sources can beexpressed as,

I _(ES1) =I _(dc) ·d ₁  (12)

I _(ES2) =I _(dc) ·d ₂  (13)

The three-phase AC power from the grid can be expressed as follows,

P _(ac)=√{square root over (3)}V _(s,rms) ·I _(s,rms)·cos(θ)  (14)

Where, V_(s,rms) is the line-to-line grid voltage; I_(s,rms) is the gridline current; and θ is the angle between the positive-sequence componentof the grid voltage and line current.

The power factor of the converter is controlled by adjusting θ. Thereare multiple modulation schemes that can be used for controlling the CSC306—one approach being to use a space-vector PWM (SVPWM) technique. ForSVPWM control, the magnitude of the ac-side line current can beexpressed as follows,

$\begin{matrix}{{II}_{s,{rms}} = {\frac{1}{\sqrt{2}}{I_{dc} \cdot m_{i}}}} & (15)\end{matrix}$

where, m_(i) is the modulation index for the CSC which can range from aminimum of 0 to a maximum of 1.

Substituting eq. 15 into eq. 14, yields,

$\begin{matrix}{P_{ac} = {\sqrt{\frac{3}{2}}{V_{s,{rms}} \cdot I_{dc} \cdot m_{i} \cdot {\cos(\theta)}}}} & (16)\end{matrix}$

If losses are neglected, the expression P_(ac)=V_(d)·I_(dc) can besubstituted into eq. 16 yielding the following expression for the dccomponent of the dc-link voltage,

$\begin{matrix}{V_{d} = {\sqrt{\frac{3}{2}}{V_{s,{rms}} \cdot m_{i} \cdot {\cos(\theta)}}}} & (17)\end{matrix}$

where, V_(d) is the DC voltage component of the dc-link voltage.

Assuming negligible resistance on the DC-side of the converter, as wellas negligible losses, the AC and DC powers can be related by thefollowing expression,

P _(ac) =P _(ES1) +P _(ES2)  (18)

Eq. 10 and 11 can be substituted into eq. 18. The result is equated withthe expression, P_(ac)=V_(d)·I_(dc). This expression is then re-arrangedyielding an alternate expression for V_(d),

V _(d) =d ₁ ·V _(ES1) +d ₂ ·V _(ES2)  (19)

The above equations provide an overview of the basic relations governingthe operation of the electric powertrain during charging and V2Goperation. The developed equations are referred to in the followingsections.

Boost-Mode Charging

In boost-mode charging, the sum of the emfs of energy storage elements 1and 2 is greater than the DC-component of the emf generated by the CSCat the maximum modulation index for the design,

V _(ES1) +V _(ES2) >V _(d)(m _(i) =m _(i,max))  (21)

where, V_(d) is defined in eq. 17 and m_(i,max) is typically near 1.

In this operating case, the modulation index can be held constant at themaximum value. The charging currents for energy storage element 1 andelement 2 are controlled by adjusting duty ratio d₁ and d₂.

Simulation cases 3, 4, 5 and 6 correspond to this operating case. Forsimulation results, please refer to diagrams 1700, 1800, 1900, and 2000of FIG. 17, FIG. 18, FIG. 19, FIG. 20. For a high-level description ofthe simulation cases refer to Table 1.

In Cases 3, 4 and 5 the vehicle is charged at 70 kW with power factorsof 0.95 lagging, 0.95 leading and unity power factor, respectively. Theenergy storage elements are each at 450 V. These cases exhibit similarbehaviour on the dc-side of the converter which can be observed whencomparing plots c) to g) between FIG. 17, FIG. 18 and FIG. 19. Thesecases differ with respect to the ac-side of the CSC, however. As can beobserved in plots a) and b) of FIG. 17 and FIG. 18, the phase currentsare displaced with respect to the phase voltages. The phase displacementbetween voltage and current corresponds to a lagging and leading powerfactor, respectively.

For Case 5, the phase currents and phase voltages are in-phase (FIG.19). In addition, the phase currents are of greater magnitude for the0.95 power factor cases (FIG. 17 and FIG. 18) compared with the unitypower factor case (FIG. 19) due to the addition of a reactive power accomponent. In Case 6, power is delivered from the vehicle to the grid atunity power factor for energy storage elements voltages of 450 V each.Case 5 and Case 6 are different in that Case 6 is a V2G operating modecase whereas Case 5 is a charging operating mode case.

Therefore, comparing FIG. 19 and FIG. 20, the phase currents are 180degrees displaced from the corresponding phase voltages in Case 6 andconversely the phase currents are in-phase with the corresponding phasevoltages in Case 5. In addition, the dc-link voltage is of negativepolarity in plot d) for the V2G case, Case 6.

Buck-Mode Charging

In buck-mode charging, the sum of the emfs of energy storage elements 1and 2 is less than the DC-component of the emf generated across theDC-terminals of the CSC at the maximum modulation index of the design,m_(i)=m_(i,max),

V _(es1) +V _(es2) <V _(d)(m _(i) =m _(i,max))  (20)

where, V_(d) is defined in eq. 19 and m_(i,max) is typically near 1.

In this operating case, the duty ratios (d₁ and d₂) can be held constantat a maximum value. The power is then controlled by adjusting themodulation index of the CSC. Simulation cases 1, 2 and 7 correspond tothis operating case. For simulation results, please refer to diagrams1500, 1600, and 2100 of FIG. 15, FIG. 16 and FIG. 21. For a descriptionof the simulation cases refer to Table 1.

In Cases 1 and 2 the vehicle is charged at 60 kW at unity power factor.In both cases, the energy storage element 2 is at a voltage of 300 V. InCase 1, energy storage element 1 is at a voltage of 300 V and in Case 2energy storage element 1 is at a voltage of 325 V. In Case 1, energystorage element 1 is maintained in the circuit by setting the modulationindex to a maximum value of 1 as observed in plot g) of FIG. 17. In Case2, as shown in FIG. 16, a form of voltage balance control is implementedsuch that equal power is delivered to energy storage element 1 andelement 2.

By way of this voltage balance control, energy storage element 1 isswitched in and out of the circuit (i.e. the modulation index is <1)generating an equivalent voltage of 300 V for the upper charging stage.This switching of energy storage element 1 can be observed in plot g) ofFIG. 16 and its impact to the motor winding voltage can be observed bycomparing plot f) in FIG. 15 and FIG. 16. Case 7 is similar to Case 1with the exception that Case 7 involves V2G operation and 70 kW of powerexchange (compared with the 60 kW of power being exchanged in Case 1).

As can be observed, the magnitude of the ac line side currents (plot b)as well as dc-side currents (plot c and plot e) are greater for Case 7compared to Case 1. In addition, the ac line currents are 180 degreesout of phase with respect to the corresponding line side voltages forCase 7. Additionally, the dc-side voltages (plot d) is of oppositepolarity for Case 7 compared with Case 1.

Energy Balance Control

In order to operate with two independent energy storage elements a formof energy balance control is required.

Some possible implementations include, voltage balance control andcirculating current control.

A possible implementation of the voltage balance control is detailed inthe following section for illustrative purposes.

Example of a Voltage Balance Control Solution

In a preceding section, eq. 10 and 11 were derived which can be used tocalculate the power delivered to energy storage element 1 and 2. Theequations are repeated here for readability reasons,

P _(ES1) =I _(dc) ·V _(ES1) ·d ₁

P _(ES2) =I _(dc) ·V _(ES2) ·d ₂

If P_(ES1)=P_(ES2) are equal then, eq. 10 and 11 can be equated whichresults in the following,

V _(ES1) ·d ₁ =V _(ES2) ·d ₂  (22)

If energy storage element 1 has a greater emf then energy storageelement 2, then the duty ratios can be set such that,

$\begin{matrix}{d_{1} = {\frac{V_{{ES}\; 2}}{V_{{ES}\; 1}} \cdot d_{2}}} & (23)\end{matrix}$

By reducing d₁ by the ratio of the emf voltages equal power is deliveredto the two energy storage elements. Note, this is just one possibleapproach for ensuring equal energy is delivered to the two energystorage elements. It should be noted that another approach would be todeliver unequal power to the two energy storage elements. This could beused to equalize the energy storage element voltages, for instance.

Interleaving

Due to the structure of the dual-inverter drive it is possible tointerleave the gating signals of:

-   -   The switches of VSC 1 with respect to those of VSC 2 which        interface the same motor windings    -   The switches of the phases of the traction inverter 1 (or        equivalently VSC 1)    -   The switches of the phases of the traction inverter 2 (or        equivalently VSC2)

Interleaving the gating signals to the switches of VSC 1 with respect tothose of VSC 2 which interface the same motor windings is advantageousas it reduces the peak ripple current in the winding currents.Interleaving the gating signals to the switches of the VSC phases withrespect to each other is advantageous as it reduces the peak ripplecurrent into the energy storage elements.

Additionally, the result of both types of interleaving is a reduction inthe peak ripple dc link current.

This reduction in ripple current has several advantages, includingreduced peak currents, reduced high-frequency current into the energystorage elements and reduced harmonic current injected into the ac grid.By reducing the harmonic current injected into the ac grid, it ispossible to reduce the size of the ac filter, for instance. Also, sincethe switching frequency choice is influenced in some embodiments by thepeak ripple current it is possible through this interleaving to reducethe switching frequencies, for instance.

One method of generating the gating signals is to compare the dutycycles corresponding to the switches against a carrier such as asawtooth carrier. The output of this comparison is then delivered to theswitches. With a method such as this, the interleaving of the gatingsignals can be achieved by phase-shifting the sawtooth carriers.

For instance, to interleave the three gating signals of the phases ofthe traction inverter 1 with respect to each other the carriers can bephase-shifted by 120 degrees each with respect to each other. Similarly,to interleave the three gating signals of the phases of the tractioninverter 2 with respect to each other the carriers can be phase-shiftedby 120 degrees each with respect to each other To interleave the gatingsignals of the switches of VSC1 with respect to those of VSC 2 whichinterface the same motor winding, the carriers can be phase shifted by180 degrees in some embodiments. Note this is only one such way toperform the interleaving of the gating signals.

In summary, the controller can interleave the switching of the three ormore phases of the first VSC and of the second VSC to reduce currentharmonics.

The controller can interleave the switching of the first and second VSC(314 and 316) switches to reduce current harmonics.

The controller can also ensure no torque production in the motor driveduring charging by ensuring the motor winding currents are dc and equal.

The controller is able to deliver different power to the energy storageelement or elements of the first VSC 314 and the energy storage elementor energy storage elements of the second VSC 316.

Simulation Results

To demonstrate the operating principles, simulation results areprovided. The simulated converter is presented in FIG. 13.

The input filter has been represented as a delta-connected capacitorbank. Each switch of the CSC includes or consists of an insulated-gatebipolar transistor (IGBT) and a series diode which together providesboth bi-polar blocking capability and uni-directional current conductioncapability. The energy storage elements are considered as batteries withnominal voltages of 500 V.

The motor inverters are represented as three-phase voltage sourceconverters. Each switch of the voltage source converters is an IGBT withan anti-parallel diode providing both bi-directional current conductioncapability and uni-polar voltage blocking capability. The motor isrepresented as a three-phase motor in open-winding configuration. Asummary of the main circuit parameters considered for the simulation areas follows:

AC Grid Voltage, V_(s(line-to-line))=600 V

AC Grid Reactance, L_(ac)=750 uH Rated Power of Charger, P_(conv)=70 kWFilter Capacitance, C_(f)=300 uF

Switching frequency of the CSC, f_(sw)=25.5 kHzSwitching frequency of the Dual-inverter Drive, f_(sw)=9.05 kHz

Nominal Voltage of Battery=500 V

A summary of the cases is provided below in Table 1. The results of thesimulation cases are presented in FIGS. 15 to 21.

TABLE 1 Description of Simulation Cases Battery 1 Battery 2 ChargingGrid Voltage EMF EMF Power Power Case Mode (Vrms) (V) (V) (kW) Factor* 1Charging 600 300 300 60 1 2 Charging 600 325 300 60 1 3 Charging 600 450450 70 0.95 4 Charging 600 450 450 70 −0.95 5 Charging 600 450 450 70 16 V2G 600 450 450 70 1 7 V2G 600 300 300 70 1 *Note, a +ve sign denotesa lagging power factor and a −ve sign denotes a leading power factor.

FIG. 15 or Case 1, illustrates the buck mode operating case, chargingmode and equal power being delivered to ES1 and to ES2. The chargingpower is approximately 60 kW and the power factor is equal to 1. Thecharging power and power factor can be determined from the plots bycomparing the system voltages with the ac line currents.

FIG. 16 or Case 2, illustrates the buck mode operating case, chargingmode, and a differential power being delivered to ES1 and to ES2. Thecharging power is approximately 60 kW and the power factor is equalto 1. The charging power and power factor can be determined by comparingthe system voltages with the ac line currents. Comparing FIG. 15 andFIG. 16 it can be observed that the same average power is beingdelivered to the vehicle, however the distribution of this power to thetwo energy storages, ES1 and ES2, is different. In FIG. 15 the samepower is being delivered to the energy storage elements. In FIG. 16,more power is being delivered to ES2 and less power is delivered to ES1compared to that in FIG. 15.

FIG. 17 or Case 3, illustrates the boost mode operating case, chargingmode, and equal power being delivered to ES1 and to ES2. The chargingpower is approximately 70 kW and the power factor is equal to 0.95. Thecharging power and power factor can be determined by comparing thesystem voltages with the ac line currents.

FIG. 18 or Case 4, illustrates the boost mode operating case, chargingmode, and equal power being delivered to ES1 and to ES2. The chargingpower is approximately 70 kW and the power factor is equal to −0.95. Thecharging power and power factor can be determined by comparing thesystem voltages with the ac line currents.

FIG. 19 or Case 5, illustrates the boost mode operating case, chargingmode, and equal power being delivered to ES1 and to ES2. The chargingpower is approximately 70 kW and the power factor is equal to 1. Thecharging power and power factor can be determined by comparing thesystem voltages with the ac line currents. The cases of FIG. 17, FIG. 18and FIG. 19 are similar except that for the change in the power factor.In FIG. 17, reactive power is being absorbed from the grid, in FIG. 18reactive power being delivered to the grid and in FIG. 19 no reactivepower is being exchanged with the grid. This can be observed incomparing the phase angle of the phase currents with respect to thephase voltages. When the phase angle of the phase currents is leading,reactive power is being delivered to the grid. When the phase angle islagging, reactive power is being absorbed from the grid. When the phaseangles are in-phase, no reactive power is being exchanged. Thereforethese cases illustrate the ability to control the power factorindependently of the power being exchanged between the vehicle and thegrid.

FIG. 20 or Case 6, illustrates the boost mode operating case, V2G mode(or equivalently discharge mode), and equal power being delivered to ES1and to ES2. The charging power is approximately 70 kW and the powerfactor is equal to 1. The charging power and power factor can bedetermined by comparing the system voltages with the ac line currents.

FIG. 21 or Case 7, illustrates the buck mode operating case, V2G mode(or equivalently discharge mode), and equal power being delivered to ES1and to ES2. The charging power is approximately 70 kW and the powerfactor is equal to 1. The charging power and power factor can bedetermined by comparing the system voltages with the ac line currents.

In all simulation cases, interleaving of the gating of the switches ofVSC 1 with respect to those of VSC 2 which interface the same motorwindings is performed. Additionally, the interleaving of the gating ofthe switches of the phases of VSC1 is performed. Additionally, theinterleaving of the gating of the switches of the phases of VSC2 isperformed.

ALTERNATE EMBODIMENTS Single-Phase AC Topology Variant

An alternate more restricted embodiment allowing only for bidirectionalcharging from a single phase ac grid is provided in FIG. 22. The CSConly has two phases and 4 switches in this alternate embodiment.

Uni-Directional Topology Variant

An alternate embodiment that is more restrictive, allowing only foruni-directional power flow from the grid to the electric vehicle (i.e.no V2G capability) is presented in FIG. 23. This alternate embodiment issimilar to the embodiment of FIG. 3, however, the polarity inversionmodule has been omitted. Possible implementations of the CSC switchesmay be involve a combination of IGBT and series diode or alternativelyIGCTs, for example.

Bi-Directional Topology Variant with SCR Front-End

The current source converter front-end can also be realized by a siliconcontrolled rectifier (SCR). This realization would restrict theoperating range and would impact the design of the three-phase AClow-pass filter.

An alternate embodiment that is more restrictive, allowing only foruni-directional power flow from the grid to the electric vehicle (i.e.no V2G capability) is presented in FIG. 16. This alternate embodiment issimilar to the embodiment of FIG. 3, however, the polarity inversionmodule has been omitted. Possible implementations of the CSC switchesmay be involve a combination of IGBT and series diode or alternativelyIGCTs, for example.

FIG. 24 is a method diagram of a method 2400 for operating an integratedthree-phase ac charger for vehicle applications with dual-inverterdrive, according to some embodiments, having steps 2402, 2404, and 2406.

FIG. 25 is a computing device diagram of an example computing device2500 that can be used for controlling gating to implement a method foroperating an integrated three-phase ac charger for vehicle applicationswith dual-inverter drive, according to some embodiments.

The computing device 2500 can include a gating signal controller devicethat includes a computer processor 2502, a computer memory 2504, aninput/output interface 2506, and a network interface 2508. The computingdevice 2500 can be coupled to the switches described herein to controlone or more gating aspects of the switches to control the operation ofthe switches.

Machine-interpretable instructions may be stored in memory 2504,including switch control sequences, and these may be updated or modifiedfrom time to time based on updates received at interfaces 2506 or 2508.

The term “connected” or “coupled to” may include both direct coupling(in which two elements that are coupled to each other contact eachother) and indirect coupling (in which at least one additional elementis located between the two elements).

Although the embodiments have been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade herein without departing from the scope. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification.

As one of ordinary skill in the art will readily appreciate from thedisclosure, processes, machines, manufacture, compositions of matter,means, methods, or steps, presently existing or later to be developed,that perform substantially the same function or achieve substantiallythe same result as the corresponding embodiments described herein may beutilized. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

As can be understood, the examples described above and illustrated areintended to be exemplary only.

1. A powertrain for an electric vehicle or a hybrid-electric vehicleproviding integrated three-phase AC charging when coupled to an AC grid,the powertrain comprising: a dual inverter drive system including anupper charging stage including a first energy storage and a firstvoltage source converter (VSC1), a lower charging stage including asecond energy storage and a second voltage source converter (VSC2),coupled to an open wound motor coupled between the first voltage sourceconverter and the second voltage source converter, the open wound motorhaving three or more motor windings each coupled to a corresponding ACterminal of each of the first voltage source converter and the secondvoltage source converter; a current source converter (CSC) includingthree CSC AC phase terminals for coupling with the AC grid, a positiveCSC DC terminal coupled to the upper charging stage at a positive VSC1DC terminal, and a negative CSC terminal coupled to the lower chargingstage at a negative VSC2 DC terminal; and the CSC including a firstcircuit leg, a second circuit leg, and a third circuit leg, each circuitleg corresponding to a corresponding CSC AC phase terminal of the threeCSC AC phase terminals, each circuit leg including at least one upperswitch coupled to a corresponding CSC AC phase terminal and the positiveCSC DC terminal, and at least one lower switch coupled to acorresponding CSC AC phase terminal and the negative CSC DC terminal,wherein each of the upper and lower switches are controlled by gatecontrol signals, which when only one upper switch is in an on-state,that switch will conduct a current equal to a sum of winding currents ofthe three or more motor windings, and when only one lower switch isoperated, that switch will conduct a current equal to the sum of thewinding currents; wherein the gate control signals are used to controlenergy flow between the AC grid and the electric vehicle or thehybrid-electric vehicle.
 2. The powertrain of claim 1, wherein thepowertrain resides within the electric vehicle or the hybrid-electricvehicle and the open wound motor is operable to provide both locomotionand to facilitate the energy flow between the AC grid and the electricvehicle or the hybrid-electric vehicle free of a separate AC/DCconversion circuit when the open wound motor is not being used toprovide locomotion, the open wound motor including magnetic componentswhich are utilized both for providing locomotion and facilitating theenergy flow.
 3. The powertrain of claim 2, wherein a controller circuitis configured to toggle operation of the open wound motor between alocomotion state and an energy flow state.
 4. The powertrain of claim 1,further comprising: a polarity inversion circuit coupled between the CSCand the upper charging stage and the lower charging stage, the polarityinversion circuit coupled to the CSC at the positive CSC DC terminal andthe negative CSC DC terminal, and the polarity inversion circuit iscoupled to the upper charging stage at the positive VSC1 DC terminal,and coupled to the lower charging stage at a negative VSC2 DC terminal;wherein the polarity inversion circuit is configured to invert apolarity of a back emf provided by the dual inverter drive such that theelectric vehicle or the hybrid-electric vehicle is able to provide powerto the AC grid.
 5. The powertrain of claim 4, wherein the polarityinversion circuit is coupled to the upper charging stage at the negativeVSC1 DC terminal and to the lower charging stage at a positive VSC2 DCterminal, and includes at least one switch that interfaces the CSC withthe dual inverter drive, with the polarity inversion circuit having afirst state and a second state; the first state coupling the positiveCSC DC terminal and the positive VSC1 DC terminal, and coupling thenegative CSC DC terminal and the negative VSC2 DC terminal; and a secondstate coupling the positive CSC DC terminal and the negative VSC1 DCterminal, and coupling the negative CSC DC terminal and the positiveVSC2 DC terminal; wherein the in the first state, power is directed tothe electrical vehicle or the hybrid electric vehicle and the in thesecond state, power is directed to the AC grid.
 6. The powertrain ofclaim 4, wherein the polarity inversion circuit includes at least oneswitch and interfaces the CSC with the dual inverter drive, with thepolarity inversion circuit having a first state and a second state; thefirst state coupling the positive CSC DC terminal and the positive VSC1DC terminal, and coupling the negative CSC DC terminal and the negativeVSC2 DC terminal; and a second state coupling the positive CSC DCterminal and the negative VSC2 DC terminal, and coupling the negativeCSC DC terminal and the positive VSC1 DC terminal; wherein the in thefirst state, power is directed to the vehicle and the in the secondstate, power is directed to the grid.
 7. The powertrain of claim 4,where the polarity inversion circuit includes a mechanical switch ofdouble pole single throw type or a switch of double pole double throwtype.
 8. The powertrain of claim 4, wherein the polarity inversioncircuit consists of at least four semiconductor switches with eachswitch of the at least four semiconductor switches coupling one CSC DCterminal to one VSC DC terminal.
 9. The powertrain of claim 4, whereineach phase of the CSC is associated with two switches, an upper switchcorresponding to the phase and a lower switch corresponding to thephase, each of the upper switch and the lower switch corresponding tothe phase comprising a first and a second series connected sub-switcheswith an accessible mid-point, the first sub-switch providing positivevoltage blocking capability and the second sub-switch providing negativevoltage blocking capability; wherein, the polarity inversion circuitincludes a first three phase switch network and a second three phaseswitch network, with each three phase switch network including at leastfour switches, three switches for each phase and one master switch thatis to controllable; wherein the positive CSC DC terminal and thepositive VSC1 DC terminal are electrically bonded, and the negative CSCDC terminal and the negative VSC2 DC terminal are electrically bonded;and wherein the first three phase switch network couples the mid-pointof the three upper sub-switches to the dual inverter drive; wherein thesecond three phase switch network couples the mid-point of the threelower sub-switches to the dual inverter drive; wherein the polarityinversion circuit has a first state and a second state: in the firststate, the first and second master control switches are controlled to beoff and the first and second phase switch network are not active; in thesecond state, the first and second master control switches arecontrolled to be on and the first and second phase switch network areactive; wherein in the first state, power is directed to the vehicle;and wherein in the second state, power is directed to the AC grid. 10.The powertrain of claim 9, wherein the first three phase switch networkis coupled to the negative VSC1 DC terminal, and the second three phaseswitch network is coupled to the positive VSC2 DC terminal or whereinthe first three phase switch network is coupled to the negative VSC2 DCterminal, and the second three phase switch network is coupled to thepositive VSC1 DC terminal. 11-20. (canceled)
 21. A method for integratedthree-phase AC charging on an electric vehicle or a hybrid-electricvehicle coupled to an AC grid, the method comprising: providing a dualinverter drive system including an upper charging stage including afirst energy storage and a first voltage source converter (VSC1), alower charging stage including a second energy storage and a secondvoltage source converter (VSC2), coupled to an open wound motor coupledbetween the first voltage source converter and the second voltage sourceconverter, the open wound motor having three or more motor windings eachcoupled to a corresponding AC terminal of each of the first voltagesource converter and the second voltage source converter; providing acurrent source converter (CSC) including three CSC AC phase terminalsfor coupling with the AC grid, a positive CSC DC terminal coupled to theupper charging stage at a positive VSC1 DC terminal, and a negative CSCterminal coupled to the lower charging stage at a negative VSC2 DCterminal the CSC including a first circuit leg, a second circuit leg,and a third circuit leg, each circuit leg corresponding to acorresponding CSC AC phase terminal of the three CSC AC phase terminals,each circuit leg including at least one upper switch coupled to acorresponding CSC AC phase terminal and the positive CSC DC terminal,and at least one lower switch coupled to a corresponding CSC AC phaseterminal and the negative CSC DC terminal; and controlling, through gatecontrol signals, energy flow between the AC grid and the electricvehicle or the hybrid-electric vehicle by operating the upper and lowerswitches which when only one upper switch is in an on-state, that switchwill conduct a current equal to a sum of winding currents of the threeor more motor windings, and when only one lower switch is operated, thatswitch will conduct a current equal to the sum of the winding currents.22. The method of claim 21, wherein the dual inverter drive system andthe current source converter are components of a powertrain that resideswithin the electric vehicle or the hybrid-electric vehicle and the openwound motor is operable to provide both locomotion and to facilitate theenergy flow between the AC grid and the electric vehicle or thehybrid-electric vehicle free of a separate AC/DC conversion circuit whenthe open wound motor is not being used to provide locomotion, the openwound motor including magnetic components which are utilized both forproviding locomotion and facilitating the energy flow.
 23. The method ofclaim 22, wherein a controller circuit is configured to toggle operationof the open wound motor between a locomotion state and an energy flowstate.
 24. The method of claim 21, further comprising: providing apolarity inversion circuit coupled between the CSC and the uppercharging stage and the lower charging stage, the polarity inversioncircuit coupled to the CSC at the positive CSC DC terminal and thenegative CSC DC terminal, and the polarity inversion circuit is coupledto the upper charging stage at the positive VSC1 DC terminal, andcoupled to the lower charging stage at a negative VSC2 DC terminal; andinverting, by the polarity inversion circuit, a polarity of a back emfprovided by the dual inverter drive such that the electric vehicle orthe hybrid-electric vehicle is able to provide power to the AC grid. 25.The method of claim 24, wherein the polarity inversion circuit iscoupled to the upper charging stage at the negative VSC1 DC terminal andto the lower charging stage at a positive VSC2 DC terminal, and includesat least one switch that interfaces the CSC with the dual inverterdrive, with the polarity inversion circuit having a first state and asecond state; the first state coupling the positive CSC DC terminal andthe positive VSC1 DC terminal, and coupling the negative CSC DC terminaland the negative VSC2 DC terminal; and a second state coupling thepositive CSC DC terminal and the negative VSC1 DC terminal, and couplingthe negative CSC DC terminal and the positive VSC2 DC terminal; whereinthe in the first state, power is directed to the electrical vehicle orthe hybrid electric vehicle and the in the second state, power isdirected to the AC grid.
 26. The method of claim 24, wherein thepolarity inversion circuit includes at least one switch and interfacesthe CSC with the dual inverter drive, with the polarity inversioncircuit having a first state and a second state; the first statecoupling the positive CSC DC terminal and the positive VSC1 DC terminal,and coupling the negative CSC DC terminal and the negative VSC2 DCterminal; and a second state coupling the positive CSC DC terminal andthe negative VSC2 DC terminal, and coupling the negative CSC DC terminaland the positive VSC1 DC terminal; wherein the in the first state, poweris directed to the vehicle and the in the second state, power isdirected to the grid.
 27. The method of claim 24, where the polarityinversion circuit includes a mechanical switch of double pole singlethrow type or a switch of double pole double throw type.
 28. The methodof claim 24, wherein the polarity inversion circuit consists of at leastfour semiconductor switches with each switch of the at least foursemiconductor switches coupling one CSC DC terminal to one VSC DCterminal.
 29. The method of claim 24, wherein each phase of the CSC isassociated with two switches, an upper switch corresponding to the phaseand a lower switch corresponding to the phase, each of the upper switchand the lower switch corresponding to the phase comprising a first and asecond series connected sub-switches with an accessible mid-point, thefirst sub-switch providing positive voltage blocking capability and thesecond sub-switch providing negative voltage blocking capability;wherein, the polarity inversion circuit includes a first three phaseswitch network and a second three phase switch network, with each threephase switch network including at least four switches, three switchesfor each phase and one master switch that is to controllable; whereinthe positive CSC DC terminal and the positive VSC1 DC terminal areelectrically bonded, and the negative CSC DC terminal and the negativeVSC2 DC terminal are electrically bonded; and wherein the first threephase switch network couples the mid-point of the three uppersub-switches to the dual inverter drive; wherein the second three phaseswitch network couples the mid-point of the three lower sub-switches tothe dual inverter drive; wherein the polarity inversion circuit has afirst state and a second state: in the first state, the first and secondmaster control switches are controlled to be off and the first andsecond phase switch network are not active; in the second state, thefirst and second master control switches are controlled to be on and thefirst and second phase switch network are active; wherein in the firststate, power is directed to the vehicle; and wherein in the secondstate, power is directed to the AC grid. 30-40. (canceled)
 41. Anon-transitory machine readable medium storing machine-interpretableinstruction sets, which when executed, cause a processor to perform amethod for integrated three-phase AC charging on an electric vehicle ora hybrid-electric vehicle coupled to an AC grid, the method comprising:providing a dual inverter drive system including an upper charging stageincluding a first energy storage and a first voltage source converter(VSC1), a lower charging stage including a second energy storage and asecond voltage source converter (VSC2), coupled to an open wound motorcoupled between the first voltage source converter and the secondvoltage source converter, the open wound motor having three or moremotor windings each coupled to a corresponding AC terminal of each ofthe first voltage source converter and the second voltage sourceconverter; providing a current source converter (CSC) including threeCSC AC phase terminals for coupling with the AC grid, a positive CSC DCterminal coupled to the upper charging stage at a positive VSC1 DCterminal, and a negative CSC terminal coupled to the lower chargingstage at a negative VSC2 DC terminal the CSC including a first circuitleg, a second circuit leg, and a third circuit leg, each circuit legcorresponding to a corresponding CSC AC phase terminal of the three CSCAC phase terminals, each circuit leg including at least one upper switchcoupled to a corresponding CSC AC phase terminal and the positive CSC DCterminal, and at least one lower switch coupled to a corresponding CSCAC phase terminal and the negative CSC DC terminal; and controlling,through gate control signals, energy flow between the AC grid and theelectric vehicle or the hybrid-electric vehicle by operating the upperand lower switches which when only one upper switch is in an on-state,that switch will conduct a current equal to a sum of winding currents ofthe three or more motor windings, and when only one lower switch isoperated, that switch will conduct a current equal to the sum of thewinding currents.